The invention provides an ion sensor, which can be used even in a solution containing numerous impurities. More specifically, the invention provides an ion sensor, implanted in a living body, capable of monitoring activities in the body.
When a particular ion in solution is oxidized or reduced by an electrode, an oxidation or reduction current flows to the electrode. The value of the electric current is generally correlated to ion concentration. Thus, this principle has been utilized for developing ion sensors in many fields. For example, since many neurotransmitters are oxidized or reduced by a platinum and carbon electrode, a particular nervous tract of the brain can be simply and easily examined by implanting these microelectrodes in the brain.
Ion sensors are excellent for observing ions in a solution immediately; however, they have the problem that they are incapable of providing reliable data when in a solution containing numerous impurities likely to stick to the surface of the electrode. Particularly, in measuring a neurotransmitter of a living body by using a conventional ion sensor, organic molecules in a body fluid such as proteins stick to its electrode, and the sensor becomes incapable of measuring the neurotransmitter. This has been a serious problem because a sensor which is implanted in the body cannot be frequently taken out and re-implanted into the body.